Peer-to-peer complementary currencies can be powerful tools for promoting collaborations and building relationships on the Internet. i- WAT[13] is a proposed such currency based on the WAT System[18], a polycentric complementary currency using WAT tickets as its medium of exchange. Participants spontaneously issue and circulate the tickets as needed, whose values are backed up by chains of trust. i-WAT implements the tickets electronically by exchanges of messages signed in OpenPGP[4]. This

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... r clarifies the trust model of i-WAT, and investigates how it is related with that of PGP [17] . To implement the model by dynamically building an appropriate web of trust (WOT), the author claims that it would suffice if the behaviors of participants satisfy the following three properties: 1. mutual signing by knowing, or any two mutual acquaintances sign the public keys of each other, 2. mutual signing by participation, or the drawer and a user of an i-WAT ticket sign the public keys of each other, and 3. mutual full trust by participation, or the drawer and a user of an i-WAT ticket fully trust each other, and a recipient fully trusts the corresponding user of a ticket, in the context of PGP public key signing. Likelihood of satisfaction of these properties is supported by the (dis)incentives imposed by the semantics of i-WAT. A reference implementation of i-WAT has been developed in the form of an XMPP[6, 7] instant messaging client. We are beginning to put the currency system into practical use. * This draft is an extended version of the paper with the same title, which is to appear in the IEICE TRANS-ACTIONS on Communication in April 2005.